The light emitted by the light source is reflected by the pellicle mirror to the Mirau interference objective, at which time it is focused on the end face of the tested fiber connector. After being reflected by the end face, it will be transmitted together with the light reflected by the reflector of the Mirau interference objective through the pellicle mirror, and be shown on the computer monitor. Then the interference fringes can be observed on the screen, and the images captured by the CCD camera are to be sent to the computer through the image card for analysis.